The invention relates generally to gas turbine engines. More specifically, the invention relates to systems and methods that indicate bleed valve position.
Gas turbine engine bleed valves are used to obtain optimum efficiency while running and to avoid engine surge. The bleed valves improve efficiency by providing greater air flow through the engine. At lower power levels the additional bypass air obviates engine surge. The valves typically do not modulate, operating either in a full open or full closed position. When a bleed valve is closed, the engine forces more air through the compressor stage.
When a bleed valve fails to open from a closed position, or fails to close from an open position in response to a control system signal, engine performance suffers. If a bleed valve fails in an open position, a shortfall of power occurs since bleed air is ducted past the compressor stage making the engine less efficient. In most gas turbines, when this occurs, the engine is at its maximum allowed exhaust temperature.
To indicate bleed valve position, closed-end and open-end position switches or sensors may be employed to provide not-open and not-closed signals to an engine control system. The signals may be used for position indication and in a bleed valve discordance alarm. A discordance alarm is used to indicate when a valve, that has been instructed to transition, or stroke from either an open or closed position never reaches the destination position. The alarm indicates whether a mechanical failure has occurred in the valve or the valve operator. The valve may have failed at its initial position or during mid-stroke. Discordance alarms typically indicate either a not open or a not closed discord. However, position switches are impracticable for use on bleed valves due to the extreme operating temperatures encountered causing a high on-engine failure rate.
Due to the dynamics of bypass flow, bleed valve position affects several engine parameters that include burner (combustor) temperature, operating pressures, and high and low rotor speeds. However, these aspects are difficult to analyze and quantify for use as an indirect result of a bleed valve failure.
There is a need for a system and method to ascertain bleed valve discordances for a gas turbine engine that does not require position switches or sensors.